Control systems typically involve the control of a device, process, or system by monitoring one or more of its characteristics. Control is used, for example, to insure that output, processing, quality and/or efficiency remain within desired parameters over the course of time. In many control systems, digital data processing or other automated apparatus monitor the device, process or system and automatically adjust its operational parameters. In other control systems, such apparatus monitor the device, process or system and display alarms or other indicia of its status, health, and other characteristics, leaving responsibility for adjustment to the operator or, in acute cases, triggering safety systems designed to prevent failures. Further, such apparatus track changes in those devices, processes, or systems, including for example operator-implemented changes to their configurations.
Control is used in a number of fields. Process control, for example, is employed in the manufacturing sector for process, repetitive and discrete manufactures, though, it also has wide application in utility and other service industries. Environmental control finds application in residential, commercial, institutional and industrial settings, where temperature and other environmental factors must be properly maintained. Control is also used in articles of manufacture, from toasters to aircraft, in order to monitor and control device operation.
Modern day control systems typically include a combination of field devices, controllers, workstations and other digital data processing apparatus, the functions of which may overlap or be combined. Field devices include temperature, flow and other sensors or transmitters that measure characteristics of the subject device, process or system. They also include valves, positioners, and other actuators that mechanically, electrically, magnetically, or otherwise effect the desired control. Increasingly, field devices are of the “intelligent” variety, including, for example, an on-board processor programmed to execute typical process control functions, as described in commonly owned U.S. Pat. No. 6,788,980 (“Methods and apparatus for control using control devices that provide a virtual machine environment and that communicate via an IP network”), which is hereby incorporated by reference in its entirety.
Controllers generate settings for actuator-type field devices based on measurements from sensor-type field devices (though such control can be executed by smart field devices and other elements of the system as well). Controller operation is typically based on a “control algorithm” that maintains a controlled system at a desired level, or drives it to that level, by minimizing differences between the values measured by the sensors and, for example, a setpoint defined by the operator.
Workstations, control stations and the like are typically used to configure and monitor the process as a whole. They are often also used to execute higher-levels of process control, e.g., coordinating groups of controllers and responding to alarm conditions signaled by them.
In a food processing plant, for example, a workstation coordinates controllers that actuate conveyors, valves, and the like, to transport soup stock and other ingredients to a processing vessel. The workstation also configures and monitors the controllers that maintain the contents of that vessel at a simmer or low boil. The latter operate, for example, by comparing measurements of vapor pressure in the processing vessel with a desired setpoint. If the vessel pressure is too low, the control algorithm may call for incrementally opening the heating gas valves, thereby, driving the pressure and boiling activity upwards. As the pressure approaches the desired setpoint, the algorithm requires incrementally leveling the valves to maintain the roil of the boil.
The field devices, controllers, workstations and other components that make up a control system typically communicate over heterogeneous media. Field devices connect with controllers, for example, over dedicated “fieldbuses” operating under proprietary or industry-specific protocols. Examples of these are FoxComm™, Profibus, ControlNet, ModBus®, DeviceNet, Foundation Fieldbus, among others. The controllers themselves may be connected to one another, as well as to workstations, via backplane or other proprietary high-speed dedicated buses, such as Nodebus™. Communications among workstations and plant or enterprise-level processors may be via Ethernet networks or other Internet Protocol (IP) networks.
The safety demands on control systems vary by industry and application. While all must generally maintain operational parameters within desired ranges over time, control systems employed, for example, in the oil & gas, chemical, and power industries, to name a few, must additionally insure that controlled systems and subsystems avoid reaching states that might lead to hazard within the plant and/or its environs—e.g., fire, explosion, hazardous materials release, equipment destruction, human injury or loss of life, etc. At the same time, these “safety systems” are typically also expected to provide high availability, e.g., avoiding false trips that might lead system or subsystem shut-down (or operational down-regulation) in response to false sensor readings and/or when safety is not truly at risk. Field devices, controllers, workstations and other apparatus supporting preferred such safety systems are manufactured and sold by the assignee hereof, e.g., under its Triconex® brand label, among others.
Traditionally, safety systems communicate via cable. Thus, for example, controllers and other members of the Triconex® family of products support process and other control via triple modular redundancy (TMR)—e.g., comparing field device, controller, and/or other equipment inputs and/or outputs using two-out-of-three-voting and utilizing two or more two disparate cable paths to support communications between safety nodes.
Wireless technology is an attractive option for implementing control system communications, but current approaches invite improvement as applied to control systems in general and safety systems, by way of particular, non-limiting example.
Accordingly, an object of the invention is to provide improved methods and apparatus for safety systems, as well as other process and other control systems.
A related aspect of the invention is to provide such methods and apparatus as improve communications within such systems.
A further object is to provide robust network connections for use in safety systems, as well as other process and other control systems, for example as a replacement or supplement to existing connections between field devices, controllers, workstations, and other devices.
A related object is to provide such robust network connections utilizing wireless technology, thereby, for example, avoiding extensive cable runs and reducing the risk of damage without loss of functionality.
A still further related object is to utilize such wireless technology in manner that supports process and other control via triple modular redundancy (TMR).
A related object is to provide such connections and networks utilizing them as reduce the complexity and cost attendant to prior art process control and other control systems.